Rapid exchange dilatation catheters are becoming increasingly popular in angioplasty procedures because, unlike over-the-wire catheters that require guide wire extenders to perform a catheter exchange, the rapid exchange dilatation catheter construction enables one rapid exchange dilatation catheter to be exchanged readily for another. U.S. Pat. No. 4,762,129 to Bonzel discloses one such catheter having a guide wire lumen only at the distal segment of the catheter, for coupling the catheter and the guide wire together. The guide wire tube extends through the balloon, from the distal end of the catheter to a point proximal to the balloon. Rapid exchange and manipulation of the dilatation catheter is facilitated because the catheter segment in contact with the surface of the guide wire is only as long as the balloon.
Although conventional rapid exchange-type catheters allow rapid catheter exchange, they tend to lack stiffness along their shaft length proximal to the exchange joint, at which point, the catheter gains the benefit of the guide wire to impart stiffness to the catheter. This lack of stiffness along the proximal portion of the catheter makes it difficult to advance the catheter through the body passageway. Bonzel addresses this problem, in part, by providing an integral stabilizing means that extends from the catheter's proximal end, through the inflation lumen, to the distal end of the balloon.
The use of a stiffening wire (or mandrel) has also been proposed in a rapid exchange catheter to provide controlled stiffness where needed without diminishing flexibility in the distal section of the catheter. Such stiffening wires, however, can buckle under compressive loads and present a potential risk of perforating the catheter wall.
The invention provides an improved rapid exchange dilatation catheter which incorporates a stiffening wire wherein the likelihood of buckling and/or perforation of the catheter shaft is substantially reduced if not eliminated.
Another feature of the invention is applicable to all balloon catheters containing guide wire lumens, for example, both over-the-wire and rapid exchange catheters. In such catheters, the guide wire lumen is normally flushed prior to use with a saline/heparin mixture to prevent blood coagulation in the lumen. The guide wire lumen must be large enough to permit free movement of the catheter relative to the guide wire. The larger the gap between the guide wire lumen and the guide wire, the freer the movement, but a smaller gap reduces the catheter profile in the distal region of the catheter, thus facilitating introducing the catheter across the stenosis.
U.S. Pat. No. 5,209,728 to Kraus et al. addresses the problem of having blood enter the catheter, and discloses a catheter provided with a tip member adapted to slidably receive a specially formed guide wire, so as to ensure a liquid-tight seal between the catheter and guide wire. The liquid-tight seal is formed by bringing the inner surface of the catheter sufficiently close to the outer surface of the guide wire. Consequently, the inflation fluid is retained within the catheter, and blood is kept out of the catheter.
However, as is typically the case with over-the-wire catheters, a reduced space between the catheter and the guide wire restricts the clear movement of the guide wire relative to the catheter. Such resistance increases the tendency of the catheter to buckle when the operator attempts to advance the catheter through the body passageway. It would, therefore, be desirable to provide a flexible dilatation catheter having a stiffening wire adapted to impart stiffness to the catheter to prevent buckling as it is manipulated through the body passageway. It would also be desirable to provide such a catheter that limits the amount of blood that enters the catheter, while at the same time, facilitates the free movement of the guide wire with respect to the catheter.
The invention further provides a balloon catheter which is movable with respect to a guide wire, wherein the profile of the distal region of the catheter is reduced without a sacrifice in freedom of movement of the catheter relative to the guide wire.